Let Us Assess & Extended Activities – Solutions വിലയിരുത്താം
All ten end-of-chapter questions, each with a model answer and an animation. They cover the vibrating parts of drums, the maddalam and the bugle; the three things needed to hear; an activity plan for sound in solids; true or false; the skin instruments; astronauts on the Moon; music and noise; cutting noise pollution; the medium race; and the bell-jar experiment with an air-pressure slider. After them come the four extended activities തുടർപ്രവർത്തനങ്ങൾ: presenting your instrument, a toy exhibition, a paper-cup telephone and noise-pollution posters. The page ends with a short note on careers in sound and Resul Pookutty. All the animations are silent.
- Sound is produced by vibration കമ്പനം. Every source has a main vibrating part and associated parts (page 5).
- Sound needs a medium മാധ്യമം and cannot travel through vacuum ശൂന്യത. It travels through solids, liquids and gases (page 6).
- Speed: solids > liquids > gases (Table 8.3). It increases with temperature (page 7).
- To hear: source + medium + organ of hearing (page 8). Music comes from regular vibrations and noise from irregular ones. Noise pollution and how to reduce it are on page 9.
Question 1 · The main vibrating part of drums, maddalam and bugle
1. ചുവടെ നൽകിയിരിക്കുന്ന ശബ്ദസ്രോതസ്സുകളുടെ ഏത് പ്രധാന ഭാഗം കമ്പനം ചെയ്യുമ്പോഴാണ് ശബ്ദം ഉണ്ടാകുന്നത്? a) ഡ്രംസ് b) മദ്ദളം c) ബ്യൂഗിൾ Which main part of each of the sources of sound below vibrates to produce sound? (a) drums (b) maddalam മദ്ദളം (c) bugle
You strike a drum and a maddalam. What do you strike? A bugle is only blown. What is inside its long metal tube?
(b) Maddalam മദ്ദളം: the stretched skins (membranes) at its two ends. (The maddalam is the big barrel drum of Kathakali and panchavadyam, a cousin of the mridangam.)
(c) Bugle: the air column inside its tube. The player's lips buzz at the mouthpiece and set it vibrating.
“The metal of the bugle vibrates.” The metal tube vibrates only a little, as an associated part. The sound comes mainly from the air column, just as in a flute.
Question 2 · Source, and which two other components?
2. ശബ്ദം കേൾക്കുന്നതിന് ആവശ്യമായ ഒരു ഘടകമാണ് ശബ്ദസ്രോതസ്സ്. മറ്റു രണ്ടു ഘടകങ്ങൾ ഏതെല്ലാം? A source of sound is one component needed to hear sound. What are the other two components?
Switch the three parts on and off in the lab. Which two others, besides the source, must be “on” for the brain to light up?
Question 3 · Plan an activity: sound travels through solids
3. ഖരവസ്തുക്കളിലൂടെ ശബ്ദം പ്രേഷണം ചെയ്യും എന്ന് തെളിയിക്കുന്നതിന് ഒരു പ്രവർത്തനം ആസൂത്രണം ചെയ്യുക. Plan an activity to prove that sound travels through solids.
Use the desk activity of Fig 8.9, but make it a fair test. Listen once with your ear away from the wood and once with your ear pressed on it. Keep the tap the same both times.
Materials: a long wooden bench or desk (about 2 m), a friend, a coin (or a tuning fork).
Procedure: (1) Stand at one end of the bench, with your ear about 2 m from the other end, and ask your friend to scratch or tap that end gently with the coin. Listen. (2) Now press one ear firmly on your end of the bench and close the other ear with your hand. Your friend scratches in exactly the same way. Listen again.
Observation: with the ear in the air the scratch is faint or not heard. With the ear pressed on the wood it is heard clearly and loudly.
Conclusion: the vibrations travelled through the wood, a solid, so sound can travel through solids (and does so better than through air).
Another way: a paper-cup telephone (extended activity 3). The voice travels along the taut string, which is a solid.
Question 4 · True or false? Correct the false ones
4. താഴെക്കൊടുത്ത പ്രസ്താവനകൾ ശരിയോ തെറ്റോ എന്ന് എഴുതുക. തെറ്റുണ്ടെങ്കിൽ തിരുത്തി എഴുതുക. Write whether the statements below are true or false. If false, correct them.
- ശബ്ദം ശൂന്യതയിലൂടെ സഞ്ചരിക്കും. Sound travels through vacuum.
- വസ്തുക്കളുടെ കമ്പനം മൂലം ശബ്ദം ഉണ്ടാകുന്നു. Sound is produced by the vibration of objects.
- ഖരവസ്തുക്കളിൽ ശബ്ദവേഗം വാതകങ്ങളിലെ വേഗത്തെക്കാൾ കൂടുതലാണ്. The speed of sound in solids is greater than in gases.
- താപനില കൂടുമ്പോൾ ശബ്ദവേഗം കുറയുന്നു. The speed of sound decreases when the temperature increases.
(b) True.
(c) True. (Steel 5944 m/s, air 347 m/s, Table 8.3.)
(d) False. Correct: when the temperature increases, the speed of sound increases. താപനില കൂടുമ്പോൾ ശബ്ദവേഗം കൂടുന്നു.
Writing only “False” gets half marks at best. The question says correct the false statement: rewrite the whole sentence correctly.
Question 5 · Which instruments sound because a skin vibrates?
5. തന്നിരിക്കുന്ന സംഗീതോപകരണങ്ങളിൽ തുകൽ കമ്പനം ചെയ്യുന്നതുമൂലം ശബ്ദം ഉണ്ടാക്കുന്നവ ഏതെല്ലാം എന്ന് എഴുതുക. (വയലിൻ, ചെണ്ട, ഓടക്കുഴൽ, മൃദംഗം, വീണ, തബല) From the instruments given, write those that produce sound because a skin (leather) തുകൽ vibrates: violin, chenda, odakkuzhal, mridangam, veena, tabla.
Question 6 · Can astronauts on the Moon hear each other directly?
6. ചാന്ദ്രയാത്രികർക്ക് ചന്ദ്രോപരിതലത്തിൽ നിന്നുകൊണ്ട് നേരിട്ട് സംസാരിക്കുന്നത് പരസ്പരം കേൾക്കുവാൻ സാധിക്കുമോ? എന്തുകൊണ്ട്? Standing on the surface of the Moon, can astronauts hear each other when they talk directly? Why?
Does the Moon have an atmosphere, a layer of air? Look up at the sky in the animation: it is black even in daytime.
If two astronauts press their helmets together, they can faintly hear each other. The sound then travels through a solid (the two helmets in contact), and solids are a medium. This fits the rule perfectly: no medium, no sound; give it a medium, and sound travels.
Question 7 · One example each: musical sound and noise
7. സംഗീതസ്വരം, ഒച്ച എന്നിവയ്ക്ക് ഓരോ ഉദാഹരണം എഴുതുക. Write one example each of a musical sound സംഗീതസ്വരം and a noise ഒച്ച.
Noise: the sound of horns and engines at a traffic junction, a construction drill, or a coconut shell rubbed on a stone.
(Music comes from regular vibrations and is pleasant. Noise comes from irregular vibrations and is unpleasant.)
Question 8 · Two ways to reduce noise pollution
8. ശബ്ദമലിനീകരണം കുറയ്ക്കാൻ രണ്ട് മാർഗങ്ങൾ നിർദേശിക്കുക. Suggest two ways to reduce noise pollution.
• Do not use air horns in vehicles, and keep vehicle silencers working properly.
• Plant many trees along roads and around buildings.
• Use box-type loudspeakers instead of horn-type ones. Do not use loudspeakers in public places before 6 am or after 10 pm.
• Avoid loud sounds near hospitals, schools and courts.
• Workers in mines and on construction sites should use ear muffs, and people near powerful machines should use ear plugs.
Question 9 · Highest and lowest speed of sound
9. ചുവടെ നൽകിയവയിൽ ഏതിലാണ് ശബ്ദത്തിന് ഏറ്റവും കൂടിയ വേഗം ഉള്ളത്? കുറഞ്ഞ വേഗമോ? a) ഖരം b) വാതകം c) ശൂന്യത d) ദ്രാവകം In which of the following does sound have the highest speed? The lowest? (a) solid (b) gas (c) vacuum (d) liquid
Race a sound pulse 1 km through each one. Careful with (c): can sound even start in a vacuum?
Speeds from Table 8.3: steel 5944 m/s, pure water 1485 m/s, air 347 m/s. Time = 1000 m ÷ speed.
Order: solid > liquid > gas. In (c) vacuum sound cannot travel at all, so it has no speed there. It is not the “lowest speed” answer.
Choosing “vacuum” as the lowest. A speed of zero means sound does not travel at all. The question asks where sound travels slowest, and that is a gas.
Question 10 · Explain the bell-jar experiment
10. ശബ്ദത്തിന് സഞ്ചരിക്കാൻ ഒരു മാധ്യമം ആവശ്യമാണെന്ന് തെളിയിക്കുവാനുള്ള ബെൽജാർ പരീക്ഷണം വിശദമാക്കുക. Explain the bell-jar experiment that proves sound needs a medium to travel.
Four things to say: the set-up, what you hear at first, what happens as the air is pumped out (and what you still see), and what happens when the air is let back in. Then the conclusion.
Step 1: switch the bell on. The hammer strikes the gong and we hear the bell clearly.
Step 2: start the vacuum pump. As the air is removed, the sound becomes fainter and fainter.
Step 3: when nearly all the air is removed, we can still see the hammer striking the gong, but we hear almost no sound. (A faint sound may still escape through the plate and the wires.)
Step 4: let the air back into the jar. The sound is heard again.
Conclusion: sound needs a medium to travel. It cannot travel through vacuum.
Extended activity 1 · Play your instrument and explain how it works
1. നിങ്ങൾ ഉപകരണസംഗീതം പഠിച്ചിട്ടുണ്ടെങ്കിൽ ആ ഉപകരണത്തിന്റെ വാദനം ക്ലാസിൽ അവതരിപ്പിച്ച് അതെങ്ങനെയാണ് പ്രവർത്തിപ്പിക്കുന്നതെന്ന് വിശദമാക്കൂ. If you have learnt to play an instrument, play it in class and explain how it works.
- Name the instrument (Malayalam and English) and the family: string, skin (drum), wind or reed.
- Play a short piece, 30 seconds is enough, at a comfortable volume.
- Point to the main vibrating part and the associated parts (use the card above).
- Show how you change the sound: tighten or press a string, close holes, strike harder or softer.
- End with one care tip for the instrument, and take questions.
Extended activity 2 · A sound-toy exhibition
2. ശബ്ദമുണ്ടാക്കുന്ന വിവിധതരം കളിപ്പാട്ടങ്ങൾ നിർമ്മിച്ച് ക്ലാസിൽ ഒരു പ്രദർശനം സംഘടിപ്പിക്കുക. Make different kinds of sound-making toys and hold an exhibition in class.
Put a label card like these next to each toy. Each one says what it is made of, how to make it, and what vibrates.
🍃 Ola-peepi ഓലപ്പീപ്പി
Made of: a strip of tender coconut or palm leaf.
How: roll the strip into a long cone and pin it with a thorn or stick. Press the narrow end flat.
What vibrates: the pressed leaf at the narrow end. The cone makes it louder.
📄 Paper whistle പേപ്പർവിസിൽ
Made of: a small sheet of paper.
How: fold it in half, tear a small hole at the fold, open it slightly and hold it between two fingers at your lips. Blow at the hole.
What vibrates: the thin paper at the edge of the hole.
🥥 Chiratta-veena ചിരട്ടവീണ
Made of: half a coconut shell, a thin wooden or card cover, a stick, a nylon string and a bow.
How: cover the shell, fix the stick through it, stretch the string from the stick to the shell and play with the bow.
What vibrates: the string (main part), plus the shell, the cover and the air inside.
🥤 Straw flute (pipi)
Made of: a paper drinking straw.
How: flatten one end and cut it into a V. Press it between your lips and blow.
What vibrates: the two flaps of the V, then the air column in the straw. A shorter straw gives a higher note.
🎸 Rubber-band guitar
Made of: a small open box, 4 rubber bands of different thickness, two pencils.
How: stretch the bands over the box and slide the pencils under them as bridges (Fig 8.2). Pluck.
What vibrates: the bands (main part), plus the box and the air inside.
🥁 Balloon drum
Made of: a tin or a plastic cup, a balloon and a rubber band.
How: cut the neck off the balloon, stretch it tightly over the open end and fix it with the rubber band. Tap with a pencil.
What vibrates: the stretched balloon skin, plus the air inside.
Extended activity 3 · Paper-cup telephones (Fig 8.22)
3. പേപ്പർ കപ്പുകളും ചരടുകളും ഉപയോഗിച്ച് കളിപ്പാട്ട ടെലിഫോണുകൾ നിർമ്മിച്ച് പ്രവർത്തിപ്പിച്ചു നോക്കൂ. Make toy telephones using paper cups and strings, and try them out.
- You need: two paper cups per phone, 5–10 m of thin, strong string (kite thread or fishing line works well), two matchsticks, a pin or a pencil tip.
- Make a small hole in the middle of the bottom of each cup, with an adult's help.
- Push one end of the string through the hole from outside and tie it to half a matchstick inside, so it cannot slip out. Do the same with the other cup.
- Two people walk apart until the string is tight (taut). One speaks into a cup and the other holds the second cup to the ear.
- Experiments: let the string go slack; pinch it with your fingers; make the string touch a wall. Then do what the children in Fig 8.22 do: cross two phones and tie the strings together where they cross, so four people can talk.
How it works: your voice makes the bottom of the cup vibrate. The vibrations travel along the taut string, a solid medium, to the other cup, whose bottom vibrates and makes the air in it vibrate, and that reaches the listener's ear.
• Slack string: almost nothing is heard. A loose string cannot pass the to-and-fro vibrations along, so they die out.
• String pinched or touching something: the sound stops at that point. The vibrations go into the hand or the wall instead.
• Strings tied where they cross: the vibrations spread into both strings at the knot, so all the other children can hear the speaker. If the strings only cross without a knot, the second phone hears little or nothing.
Extended activity 4 · Posters against noise pollution
4. ശബ്ദമലിനീകരണത്തിന്റെ ദോഷങ്ങളെക്കുറിച്ച് ജനങ്ങളെ ബോധവൽക്കരിക്കാൻ പോസ്റ്ററുകൾ തയ്യാറാക്കുക. Prepare posters to make people aware of the harmful effects of noise pollution.
- One short, catchy slogan, in Malayalam and English if you like, readable from 3 metres away.
- One big, clear picture. Draw it yourself.
- Two or three facts: who is harmed (patients, babies, students, the elderly, birds); the effects (headache, sleeplessness, stress, hearing loss); what to do (no air horns, box-type speakers, no loudspeakers before 6 am or after 10 pm, plant trees).
- Your class and school name. Display it where people will see it: the school gate, a bus stop, the library.
Careers in sound – Resul Pookutty റസൂൽ പൂക്കുട്ടി
ചലച്ചിത്രമേഖലയിലെ ലോകോത്തര ബഹുമതിയായ ഓസ്കാർ പുരസ്കാരം മികച്ച ശബ്ദമിശ്രണത്തിലൂടെ ഇന്ത്യയ്ക്ക് നേടിത്തന്ന അതുല്യപ്രതിഭയാണ് റസൂൽ പൂക്കുട്ടി. Resul Pookutty is the outstanding talent who won India the Oscar, the world's top film award, for the best sound mixing ശബ്ദമിശ്രണം.
- Born in 1971 at Vilakkupara, Anchal, in Kollam district, Kerala.
- A sound engineer. He won the Oscar for sound mixing for Slumdog Millionaire, a British film made against an Indian background.
- Also won the British BAFTA award, the Cinema Audio Society award (USA), the Padma Shri, and many national and international awards.
- Honoured as a “Distinguished Engineer” by the Rochester Institute of Technology, New York. He was the first Asian to become a member of the sound-mixing awards committee of the Academy of Motion Picture Arts and Sciences.
Sound is a career too. People who work with what you learnt in this chapter include sound engineers and sound mixers (films, concerts, radio); audiologists ഓഡിയോളജിസ്റ്റ്, who test hearing and fit hearing aids; speech therapists; acoustic engineers, who design quiet buildings and concert halls; musicians and instrument makers; and scientists who use sound under water (SONAR) or in hospitals (ultrasound, see page 12).
- 📄 Helen Keller Wikipedia
The deafblind American writer who learned to communicate through touch and became a world-famous campaigner. - 📄 Helen Keller: Biography American Foundation for the Blind
Helen Keller's life story from the organisation she worked with for over 40 years. - 📄 Resul Pookutty Wikipedia
The sound designer from Kollam, Kerala, who won an Oscar for sound mixing on Slumdog Millionaire. - 📄 81st Academy Awards Wikipedia
The 2009 Oscars, where Slumdog Millionaire won eight awards, including Best Sound Mixing.